Adverse effects of meditation were assessed in twenty-seven long term meditators (average 4.27 years) both retrospectively (time one) and prospectively at one month (time two) and six months (time three) following a meditation retreat. At both time one and time three subjects reported significantly more positive effects than negative from meditation. However, of the twenty-seven subjects, seventeen (62.9%) reported at least one adverse effect, and two (7.4%) suffered profound adverse effects. When subjects at time one were divided into three groups based on length of practice (16.7 months; 47.1 months; 105 months) there were no significant differences in adverse effects. How the data should be interpreted, and their implications both for the clinical and psychotherapeutic use of meditation as a relaxation/self-control strategy, and as a technique for facilitating personal and spiritual growth, are discussed. Limitations of the study and suggestions for future research are also offered.